Patent GB-874747-A (GB)
Title: Zinc salts of mixed dialkyl dithiophosphoric acids and lubricating compositions containing them
IPC: C07F9/165
Filed: 1958-04-01
Abstract: A zinc mixed dialkyl dithiophosphate useful as an additive for lubricating oils (see Group III) is obtained by heating a mixture of at least two separately prepared different simple or homogeneous dialkyl dithiophosphoric acids with a saturated aliphatic alcohol, neutralising the resulting product with a reactive zinc compound and then stripping off any uncombined alcohol by vacuum distillation. The preferred dialkyl dithiophosphoric acid mixture is one in which one ester contains two identical alkyl radicals of 1 to 6 carbon atoms and the other ester is a different bis-ester containing two identical alkyl radicals of 3 to 10 carbon atoms.  The alcohol with which the mixture is heated is preferably a C1-6 alcohol and this alcohol may be the same as or different from either of the alcohols used in preparing the mixture of the dialkyl dithiophosphoric acids and is preferably the same as the alcohol used in preparing the bis ester of low molecular weight.  It is preferred to add a C1C6 saturated aliphatic alcohol in an amount ranging from 1% to about 15% based on the weight of the mixture of dialkyl dithiophosphoric acids and the resulting mixture is then heated usually for about 0.5 to 3 hours at a temperature depending on the boiling point of the added alcohol, e.g. in the case of isopropanol a suitable heating temperature is between about 65.6 DEG C. and the boiling point of isopropanol. After the heat treatment the mixture is preferably cooled and a reactive zinc compound, e.g. zinc oxide or hydroxide, in added with agitation and the mixture heated until neutralisation is complete.  An excess of the zinc compound is preferably employed. The mixture is finally stripped free from uncombined alcohols and other volatiles by vacuum distillation and is then filtered free from solids and cooled.  In typical examples di-methyl isobutyl carbinyl dithiophosphoric acid (or di-n-decyl dithiophosphoric acid) and di-isopropyl dithiophosphoric acid are prepared separately by heating the corresponding alcohol with phosphorus pentasulphide and are then mixed together, the mixture heated with isopropanol at 76.7 DEG C. and then reacted with zinc oxide at elevated temperature, the mixture being finally vacuum stripped and then filtered.  Examples are also given in which n-butyl alcohol and ethanol respectively are heated with a mixture of di-isobutyl carbinyl- and diisopropyl-dithiophosphoric acid and the mixture neutralised with zinc oxide.  A comparative example is also given in which a mixture of isobutylcarbinol and isopropyl alcohol is heated with P2S5 and the mixed dialkyldithiophosphoric acids neutralised with zinc oxide.ALSO:A lubricating composition comprises a hydrocarbon oil of lubricating viscosity having dissolved therein a zinc mixed dialkyl dithiophosphate obtained by heating a mixture of simple or homogeneous dialkyl dithiophosphoric acids with a saturated aliphatic alcohol, neutralising the resulting product with a reactive zinc compound and then stripping off any uncombined alcohol by vacuum distillation (see Group IV(b)).  The preferred dialkyl dithiophosphoric acid mixture is one in which one ester contains two identical C1-C6 alkyl radicals (e.g. isopropyl) and the other ester is a different bis-ester containing two identical C3-C10 alkyl radicals (e.g. isobutylcarbinyl or n-decyl).  The alcohol with which the mixture is heated is preferably a C1-C6 aliphatic alcohol, e.g. ethanol, isopropanol or n-butanol and this alcohol may be the same as or different from either of the alcohols corresponding to the alkyl radicals in the mixed dialkyl dithiophosphoric acids. Other lubricating oil additives may be present, e.g. calcium or barium petroleum sulphonates.  Reference is also made for comparative purposes to the use as lubricant additive of the zinc salt derived from a mixed dialkyl dithiophosphoric acid obtained by reacting a mixture of methyl isobutyl carbinol and isopropanol with phosphorus pentasulphide.